1. Field of the Invention
The present invention relates to a linear motor, and more particularly to a linear motor including a plurality of coil groups having different coil thicknesses and wound on a bobbin. Also, the present invention relates to a method for controlling such a linear motor and to a linear compressor equipped with such a linear motor.
2. Description of the Related Art
Generally, a motor is a device that converts electric energy into mechanical energy. Such a motor is widely used in all kinds of machines, such as compressors, blowers, pumps, etc. The motor basically comprises a case, a stator fixed to the case, and a mover rotated or linearly reciprocated by means of an electromagnetic force created between the mover and the stator.
The motors may be classified, on the basis of how the mover is operated, into a rotary motor whose mover is rotated, a linear motor whose mover is linearly reciprocated, and a vibratory motor whose mover is vibrated.
FIG. 1 is a sectional view showing a linear compressor equipped with a linear motor according to the prior art.
As shown in FIG. 1, the conventional linear compressor comprises: a hermetically sealed container 1; a compression unit 4 for compressing a gas coolant, the compression unit 4 comprising a piston 2 and a cylinder 3; and a linear motor 10 for linearly reciprocating the piston in the cylinder 3, the linear motor 10 comprising a stator 5 and a mover 6.
The stator 5 comprises: a laminated outer core 12; an inner core 14 disposed in the outer core 12 such that the inner core 14 is spaced apart from the outer core 12 by a prescribed gap distance; and a coil assembly 20 fixed to the outer core 12. The mover 6 comprises: a magnet 42 disposed between the inner core 12 and the outer core 14; and a magnet frame 44 connected between the magnet 42 and the piston 2 for transmitting linear movement of the magnet 42 to the piston 2.
The coil assembly 20 comprises: a bobbin 24; and a coil 26 wound on the bobbin 24 such that a magnetic field is created at the coil 26 when an electric voltage is applied to the coil 26. The coil is usually wound on the bobbin 24 two turns or more.
The larger the thickness of the coil 26 is, the higher efficiency of the linear motor 10 with the above-stated construction is. The higher the voltage inputted from the outside is, the larger the stroke of the piston 2, which is the distance of movement within which the piston 2 is reciprocated. The more the coil 26 is turned, the smaller the stroke of the piston 2 is.
Generally, a voltage supplied from a power supply is applied to the coil 26 with variation of approximately 15% of a prescribed value (for example, 220 V). When a high voltage exceeding the prescribed value is applied to the coil 26, the stroke of the piston 2 become too large with the result that the piston 2 may collide with peripheral components. For this reason, it is required to provide an additional auxiliary coil (not shown), which is connected to the coil 26 only when the abnormal high voltage is applied to the coil 26. In this case, the number of the turns of the whole coils is increased, whereby the excessive stroke of the piston 2 is not carried out, and thus the above-mentioned collision between the piston and the peripheral components is prevented.
In the conventional linear motor and the conventional linear compressor equipped with the linear motor, however, the number of the turns of the coil 26 is increased providing against input of the high voltage, which occurs only limitedly, with the result that the sizes of the coil assembly 20 and thus the linear motor are increased. Consequently, the production cost of the linear motor and the linear compressor equipped with the linear motor is increased.